Project Summary: Although adolescents frequently try to quit smoking cigarettes, their attempts typically end n relapse. To improve smoking cessation interventions for adolescents, more information is needed about the processes underlying relapse in this population. Social-learning models suggest that lapses, or discrete episodes of smoking following a quit attempt, are caused by dynamic, within-person processes (e.g., exposure to smoking cues). However, studies of adolescent smoking cessation have focused almost xclusively on static between-person factors (i.e., individual differences), not dynamic within-person processes. Studies of within-person processes may go beyond previous research by identifying the unique contexts surrounding smoking lapses, which could inform treatments. Accordingly, in this study, 200 adolescent smokers will intensively self-monitor an attempt to quit smoking in real-time for 3 weeks (1 week pre-quit, 2 weeks post-quit). Using ecological momentary assessment methods, adolescents will report multiple times per day on their quit experience. We will examine hypotheses arising from social-learning relapse models in this study. Specifically, we hypothesize that (a) exposure to smoking cues, such as being around other smokers, and (b) changes in motivation, outcome expectancies (e.g., beliefs that smoking will improve mood), and self-efficacy will be associated with lapses to smoking. Further, nicotine dependence level is expected to moderate the relationship between affect state/craving and lapsing, such that more dependent adolescent smokers will be more prone to lapse in situations marked by negative affect and craving, while less dependent smokers will be more likely to lapse in positive affect/social situations. The long-term goal of this study is to generate information about adolescent smoking relapse that may improve interventions for this population. Public Health Relevance: Understanding the factors underlying adolescent smoking relapse may allow for the development of improved interventions, including self-help materials that can be widely disseminated. This improvement in efficacy and reach of interventions may reduce the number of adolescents who go on to become adult smokers and, ultimately, reduce smoking-related morbidity and mortality.